The localized vibrational mode of carbon substituted at arsenic sites in ga
llium arsenide (GaAs) was measured with infrared absorption spectroscopy at
0.005 cm(-1) resolution. Well-resolved fine structures were observed, yiel
ding quantitative information on the line half widths and intensities. The
relative intensities of the isotope lines are well fitted to a probability
factor calculation using a natural abundance of 55.3% Ga-69. One explanatio
n considered is that the dipole moment due to the relative displacement of
carbon with respect to the gallium atoms has a tendency to be larger when t
he neighboring gallium atoms are heavier (Ga-71). (C) 2001 American Institu
te of Physics.